Although their findings need to be confirmed in larger studies, Ward said, ensuring that older patients "have optimal vitamin D levels may be a way to boost [their] immune function," and potentially stave off chronic disease.

Although exact estimates vary, it's not uncommon to develop transient hypocalcemia after having the thyroid removed, usually because of a concurrent drop in levels of parathyroid hormone (PTH), which plays a key role in calcium metabolism.

Some have speculated that an underlying vitamin D deficiency might increase the risk of falling calcium levels after surgery, but little research has been done.

Patrick Sheahan, MD, of South Infirmary Victoria University Hospital in Cork, and colleagues looked at data on 121 patients who had thyroidectomy. About a quarter subsequently developed hypocalcemia.

They found no links, however, between vitamin D levels before surgery and later development of low calcium.

That said, clinicians shouldn't discount the fact that vitamin D may be able to help restore calcium levels in these patients after surgery, they wrote.